Multi-anode detector with increased dynamic range for time-of-flight mass spectrometers with counting data acquisition

A method for determining the times of arrival of a first ion arrival signal and a second ion arrival signal in a time-of-flight mass spectrometer, comprising the steps of:

• providing a first electron multiplier with a first gain;
• producing from said first electron multiplier a first group of electrons in response to said first ion arrival signal;
• producing from said first electron multiplier a second group of electrons in response to said second ion arrival signal;
• providing a first anode;
• directing said first group of electrons so that said first group is received by said first anode, thereby producing a first output signal in response to said first ion arrival signal;
• directing said second group of electrons so that said second group is not received by said first anode;
• providing a second electron multiplier with a second gain greater than said first gain;
• producing from said second electron multiplier a third group of electrons in response to said second group of electrons but not in response to said first group of electrons;
• providing a second anode;
• directing said third group of electrons so that said third group is received by said second anode, thereby producing a second output signal in response to said second ion arrival signal;
• and,
• calculating the times of arrival of said first ion arrival signal and said second ion arrival signal based on said first output signal and said second output signal.

A method for combining TDC data collected from a plurality of anodes in an unequal anode detector, comprising the steps of:

• recording a histogram for each anode i from said plurality of anodes;
• determining the effective number of TOF extractions (N′xi) seen by each anode i from said plurality of anodes;
• determining the recorded number of counts (NRi) on each anode i from said plurality of anodes;
• estimating the number of impinging ions detected by each anode i from said plurality of anodes as N ~ R i = - N x ⁢ ⁢ ln ⁢ ⁢ ( 1 - N R i N x i ′ ) ;
• correcting said recorded histogram for each anode i from said plurality of anodes by substituting said estimate ÑRi;
• and,
• combining said corrected histograms into a weighted linear combination of minimal total variance.

A time-of-flight mass spectrometer, comprising:

• an ion source producing a stream of ions;
• an extraction chamber receiving a portion of said stream of ions from said ion source;
• a flight section receiving said portion of ions from said extraction chamber and accelerating said portion of ions to produce a first accelerated stream of ions and second accelerated stream of ions spatially separated from said first accelerated stream of ions;
• a detector receiving said first accelerated stream of ions and said second accelerated stream of ions from said flight section, said detector comprising:
• a first electron multiplier with a first gain for producing a first group of electrons in response to said first accelerated stream of ions and for producing a second group of electrons in response to said second accelerated stream of ions;
• a first anode for receiving said first group of electrons and for not receiving said second group of electrons, thereby producing a first output signal in response to said first accelerated stream of ions;
• a second electron multiplier with a second gain greater than said first gain for producing a third group of electrons in response to said second group of electrons but not in response to said first group of electrons;
• a second anode for receiving said third group of electrons, thereby producing a second output signal in response to said second accelerated stream of ions;
• and,
• detection circuitry connected to said first anode and said second anode for providing time-of-arrival information for said first accelerated stream of ions and said second accelerated stream of ions based on said first output signal and said second output signal;
• a data acquisition system for receiving said time-of-arrival information for said first accelerated stream of ions and said second accelerated stream of ions and for combining said time-of-arrival information into a weighted linear combination of minimum total variance.